Force reflecting haptic interfaces and associated computer hardware and software are used in a variety of systems to provide tactile sensory feedback to a user in addition to conventional visual feedback, thereby affording an enhanced man/machine interface. These systems are becoming more prevalent in such diverse areas as surgical technique training, industrial design and modeling, and personal entertainment.
Two examples of haptic interfaces for use in a desktop environment are disclosed in U.S. Pat. Nos. 5,587,937 and 6,417,638, the disclosures of which are hereby incorporated herein by reference in their entireties. Generally, haptic interfaces define a user reference point located, for example, proximate or within a volume of a user connection element such as a finger thimble or stylus configured to be donned or grasped by a user. Disposed between the user connection element and a spatial or reference ground are a series of mechanical transmission elements such as gimbals, linkages, and frames configured to permit substantially unrestricted movement of the connection element within a predetermined work volume of the haptic interface when in an unpowered state.
Based on the configuration and orientation of the transmission elements, multiple independent degrees of freedom may be provided. Depending on the particular application for the interface, each degree of freedom may be powered and/or tracked, or free, being neither powered nor tracked. For example, a degree of freedom may be powered by a motor or other actuator so that, under appropriate conditions, the interface can resist, balance, or overcome a user input force along that degree of freedom. The powered axis may be active, with force being varied as a function of system conditions, or passive, such as when a constant resistance or drag force is applied. Alternatively or additionally, a degree of freedom can be tracked using an encoder, potentiometer, or other measurement device so that, in combination with other tracked degrees of freedom, the spatial location of the reference point within the work volume can be determined relative to ground. Lastly, a degree of freedom may be free, such that a user is free to move along the degree of freedom substantially without restriction and without tracking within the limits of the range of motion. The interface, in combination with appropriate computer hardware and software, can be used to provide haptic feedback in a virtual reality environment or link a user to an actual manipulator located, for example, in a remote or hazardous environment.
Significant challenges exist in designing a force reflecting haptic interface with appropriate operational and response characteristics. For example, it is desirable that the haptic interface have low friction and weight balance such that a user's movements will not be unduly resisted and the user will not become fatigued merely by moving the connection element within the work volume. It is also desirable that the haptic interface have a high degree of resolution and be highly responsive so as to replicate, as closely as possible, an actual haptic experience. Compact size, low cost, and the interchangeability of various input interfaces are also beneficial attributes from the standpoint of commercial acceptance and appeal.
Nevertheless, the complex technology involved in a force reflecting haptic interface has hampered efforts to reduce size and cost. The architecture of such a device requires unit sizes that are larger than desirable, often because of such factors as motor placement, weight counter-balancing measures, and component size characteristics. Such large unit sizes often drive commercial costs higher, as do the unique components that are required in such a device. The complex technology has also limited the interchangeability of input interfaces, thus requiring the acquisition of a custom device with a specific input interface for each different application.
These limitations on size and cost are presently an unfortunate bar to many markets to which a force reflecting haptic interface is well-suited. For example, lower cost would make such an interface available to consumers, for use with their home personal computers. Use of a haptic interface as a peripheral device would effectively widen the bandwidth of human interaction with the computer, by providing an interface that incorporates a sense of touch, well beyond the standard two-dimensional interaction of sight and sound.
There is, therefore, a need for a force reflecting haptic interface with enhanced functionality that is compact in size and of relatively low cost, so as to be available to a broad consumer market.